Why Do Humans Have Eyebrows and Eyelashes?

As humans have evolved, our body hair and facial hair have diminished over time. But eyebrows and eyelashes remained a core part of our features. They are our foremost eye accessories, and we wax, tweeze and even dye them.

But is there a biological or functional reason we have hair above and around our eyes? Researchers and ophthalmologists believe there is.

Eyebrows Move Moisture Away from Eyes and Help Identify Individuals

The area of curved, delicate hairs above our eyes are believed to channel unwanted moisture—sweat and rain in particular—away from the eye to help keep vision clear. The shape and direction of the hairs make it easier for moisture to flow sideways around the eyes, along the side of the head. They also help to block out light and filter dust and dirt that may fall into the eyes.

Certain autoimmune diseases and hormonal imbalances, such as alopecia, hypothyroidism and lupus, can cause hair loss in the eyebrows.

Eyelashes Prevent Irritation and Act as Human Whiskers

Eyelashes are a group of hairs that grow around the edge of the eyelid. They operate as dust catchers, protecting the eye from debris that can obstruct vision or cause infection or injury. They are like human whiskers. Lashes act as sensors for objects coming close to the eye—like insects—and trigger a reflexive and protective blink.

Ivan Schwab, MD, professor of ophthalmology at University of California, Davis, says eyelashes are “unique among body hair. Healthy lashes are believed to never go gray. They are among the shortest hairs on the body with the longest lifespan. And the melanocytes (pigment cells) at the base of eyelash follicles rarely, if ever, become malignant.”

A 2015 study published in the Journal of the Royal Society Interface found that eyelashes act as air filters for the eye. The researchers, who conducted tests using man-made eye and eyelash mockups, believe that lashes reduce tear evaporation up to 50 percent, helping to keep eyes sufficiently lubricated.

Be Careful with Cosmetic Enhancements to Eyebrows and Eyelashes

Tinting eyebrows and eyelashes has grown in popularity. This practice is not regulated by the U.S. Food and Drug Administration, and experts warn that tinting eyebrows and eyelashes can be risky. Additionally, use of Latisse or Bimatropost—a form of a glaucoma drug that also is used to lengthen and thicken eyelashes—can have undesirable side effects. Darkening of the skin around the eyes and even darkening of the iris (from blue to brown, for example) are rare side effects that cannot be reversed.